Exchangeability of N Termini in the Ligand-gated Porins ofEscherichia coli
The ferric siderophore transporters of the Gram-negative bacterial outer membrane manifest a unique architecture: Their N termini fold into a globular domain that lodges within, and physically obstructs, a transmembrane porin β-barrel formed by their C termini. We exchanged and deleted the N termin...
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Published in | The Journal of biological chemistry Vol. 276; no. 16; pp. 13025 - 13033 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
American Society for Biochemistry and Molecular Biology
20.04.2001
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Online Access | Get full text |
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Summary: | The ferric siderophore transporters of the Gram-negative bacterial outer membrane manifest a unique architecture: Their N
termini fold into a globular domain that lodges within, and physically obstructs, a transmembrane porin β-barrel formed by
their C termini. We exchanged and deleted the N termini of two such siderophore receptors, FepA and FhuA, which recognize
and transport ferric enterobactin and ferrichrome, respectively. The resultant chimeric proteins and empty β-barrels avidly
bound appropriate ligands, including iron complexes, protein toxins, and viruses. Thus, the ability to recognize and discriminate
these molecules fully originates in the transmembrane β-barrel domain. Both the hybrid and the deletion proteins also transported
the ferric siderophore that they bound. The FepA constructs showed less transport activity than wild type receptor protein,
but the FhuA constructs functioned with turnover numbers that were equivalent to wild type. The mutant proteins displayed
the full range of transport functionalities, despite their aberrant or missing N termini, confirming (Braun, M., Killmann,
H., and Braun, V. (1999) Mol. Microbiol. 33, 1037â1049) that the globular domain within the pore is dispensable to the siderophore internalization reaction, and when
present, acts without specificity during solute uptake. These and other data suggest a transport process in which siderophore
receptors undergo multiple conformational states that ultimately expel the N terminus from the channel concomitant with solute
internalization. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1074/jbc.M011282200 |